Final answer:
Urine is the most typically used body fluid in workplace drug testing due to its non-invasive collection and ability to reflect ingested substances over time.
Step-by-step explanation:
The body fluid most typically used in workplace drug testing is urine. Urine testing is favored because it is non-invasive, easy to collect, and can detect a wide range of substances over an extended period of time. Substances that are ingested eventually get processed by the body and can be excreted in the urine. The reference values for blood plasma, cerebrospinal fluid (CSF), and urine for various ions suggest that urine provides a good reflection of the substances present in the body, such as sodium, potassium, and chloride. On the contrary, elements like bicarbonate are conserved by the kidneys for the body's buffering systems and are not normally excreted in urine. Therefore, for most workplace drug tests, urine samples are collected and then analyzed for the presence of drugs or their metabolites.